The present invention relates to the general field of making gas turbine casings out of composite material, and it relates more particularly to gas turbine fan retention casings for aeroengines.
In a gas turbine aeroengine, a fan casing performs several functions: it defines the air inlet passage into the engine, it supports an abradable material facing the tips of the fan blades, it supports an optional structure for absorbing sound waves for acoustic treatment at the inlet of the engine, and it incorporates or supports a retention shield. The shield constitutes a trap for retaining debris, such as ingested articles or fragments of damaged blades that are thrown outwards by centrifuging, in order to prevent them from passing through the casing and reaching other portions of the aircraft.
A fan retention casing is commonly constituted by a relatively thin wall defining the air inlet passage and supporting an abradable material overlying the path followed by the tips of the fan blades, together with the acoustic treatment coating, if any, and also by a shield structure that is fastened to the outside of this wall, level with the fan.
Proposals have already been made to make a fan retention casing out of composite material. By way of example, reference may be made to document EP 1 961 923, which describes fabricating a composite material casing of thickness that varies and that includes forming fiber reinforcement in the form of superposed layers of a fiber texture and densifying the fiber reinforcement with a matrix. More precisely, that document makes provision for using a takeup mandrel for three-dimensional weaving of the fiber texture, which texture is then wound as superposed layers onto an impregnation mandrel that presents an outside surface having a profile corresponding to the profile of the central portion of the casing that is to be made, together with two side plates that correspond to the flanges for fastening the casing. The fiber preform as obtained in that way is held on the impregnation mandrel and it is impregnated with resin prior to the resin being polymerized.
Practical implementation of that method raises the problem of transferring the fiber texture from the takeup mandrel onto the impregnation mandrel. While that winding is taking place, it is necessary in particular to ensure an adequate level of compacting on the superposed layers of fiber texture on the impregnation mandrel. The amount of compacting to which the fiber texture layers are subjected while they are being wound has a direct influence on the fiber density of the resulting preform. In particular, it must be possible to compact the layers of fiber texture both for the outside surface of the impregnation mandrel and in the corners formed between said surface and the side plates of the mandrel.
Consequently, there exists the need for a tool that enables the various layers of fiber texture to be compacted in effective and appropriate manner while they are being wound onto the impregnation mandrel.